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What do positrons have to do with dark matter?

  1. Apr 25, 2013 #1
    In referring to the recent results of the AMS experiment in the ISS:


    I'm still left wanting of understanding why the presence of an excess of positrons infiltrating the device isometrically indicates a presence of dark matter and tells me something about it.

    What I'm getting is that this positron excess is supposed to be reflective of annihilation events in the dark matter. From the article:

    But if we don't know what dark matter is, how can we say that annihilation events would produce excess positrons, or positrons at all? I don't know if I'm feeling my 2 billions dollars working for me here. Can someone enlighten me?
  2. jcsd
  3. Apr 25, 2013 #2


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    The energy believed necessary for dark particle annihilation suggests positrons must be created. The excess of positrons detected suggests particle creation events that cannot be accounted for by processes within our galaxy. It is possible they could be from extragalactic sources, but, positrons probably cannot survive the vast distances involved. That suggests a local source of unseen matter must be involved [i.e., dark matter].
    Last edited: Apr 25, 2013
  4. Apr 25, 2013 #3


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    No one claims they’ve detected dark matter because of the tiny excess of positrons detected. All they can say is that if one particular version of the WIMP (self-annihilation) hypothesis is true then they would expect some positrons. They correctly remind us these positrons may come from somewhere else, for instance, Pulsars. The WIMP models have several epicycles: Check out Neil Weiner of NYU who postulated some excess positrons from the PAMELA experiment were due to WIMP collisions. Later, Lisa Randall of Harvard added this new twist: there may be two types of WIMPS and only some small fraction of them would interact with each other via a new “dark force”. Not very likely, in my opinion, because this WIMP self-interacting epicycle would require a new complication: the “dark photon”.
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